https://phys.org/news/2018-11-mystery-particle-discovery-require-physics.html

The new result – consisting of a mysterious bump in the data at 28 GeV (a unit of energy) – has been published as a preprint on ArXiv. It is not yet in a peer-reviewed journal – but that's not a big issue. The LHC collaborations have very tight internal review procedures, and we can be confident that the authors have done the sums correctly when they report a "4.2 standard deviation significance". That means that the probability of getting a peak this big by chance – created by random noise in the data rather than a real particle – is only 0.0013%. That's tiny – 13 in a million. So it seems like it must a real event rather than random noise – but nobody's opening the champagne yet.

Many LHC experiments, which smash beams of protons (particles in the atomic nucleus) together, find evidence for new and exotic particles by looking for an unusual build up of known particles, such as photons (particles of light) or electrons. That's because heavy and "invisible" particles such as the Higgs are often unstable and tend to fall apart (decay) into lighter particles that are easier to detect. We can therefore look for these particles in experimental data to work out whether they are the result of a heavier particle decay. The LHC has found many new particles by such techniques, and they have all fitted into the standard model.